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focused wave Properties Based on A High Order Spectral Method with A Non-Periodic Boundary

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China Ocean Engineering 2015年第1期29卷 1-16页

作者：李金宣柳淑学 State Key Laboratory of Coastal and Offshore Engineering Dalian University of Technology

In this paper, a numerical model is developed based on the High Order Spectral （HOS） method with a non-periodic boundary. A wave maker boundary condition is introduced to simulate wave generation at the incident boundary in the HOS method. Based on the numerical model, the effects of wave parameters, such as the assumed focused amplitude, the central frequency, the frequency bandwidth, the wave amplitude distribution and the directional spreading on the surface elevation of the focused wave, the maximum generated wave crest, and the shifting of the focusing point, are numerically investigated. Especially, the effects of the wave directionality on the focused wave properties are emphasized. The numerical results show that the shifting of the focusing point and the maximum crest of the wave group are dependent on the amplitude of the focused wave, the central frequency, and the wave amplitude distribution type. The wave directionality has a definite effect on multidirectional focused waves. Generally, it can even out the difference between the simulated wave amplitude and the amplitude expected from theory and reduce the shifting of the focusing points, implying that the higher order interaction has an influence on wave focusing, especially for 2D wave. In 3D wave groups, a broader directional spreading weakens the higher nonlinear interactions.

关键词： focused wave high order spectral method numerical model

Numerical Comparison for focused wave Propagation Between the Fully Nonlinear Potential Flow and the Viscous Fluid Flow Models

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China Ocean Engineering 2020年第2期34卷 279-288页

作者： JIANG Sheng-chao LIU Chang-feng SUN Lei School of Naval Architecture State Key Laboratory of Structural Analysis for Industrial EquipmentDalian University of TechnologyDalian 116024China State Key Laboratory of Coastal and Offshore Engineering Dalian University of TechnologyDalian 116024China College of Ocean and Civil Engineering Dalian Ocean UniversityDalian 116023China

Numerical simulations on focused wave propagation are carried out by using three types of numerical models,including the linear potential flow,the nonlinear potential flow and the viscous fluid flow models.The wave-wave interaction of the focused wave group with different frequency bands and input wave amplitudes is examined,by which the influence of free surface nonlinearity and fluid viscosity on the related phenomenon of focused wave is investigated.The significant influence of free surface nonlinearity on the characteristics of focused wave can be observed,including the increased focused wave crest,delayed focused time and downstream shift of focused position with the increase of input amplitude.It can plot the evident difference between the results of the nonlinear potential flow and linear potential flow models.However,only a little discrepancy between the nonlinear potential flow and viscous fluid flow models can be observed,implying the insignificant effect of fluid viscosity on focused wave behavior.Therefore,the nonlinear potential flow model is recommended for simulating the non-breaking focused wave problem in this study.

关键词： focused wave linear potential flow fully nonlinear potential flow viscous fluid flow boundary element method OpenFOAM

The response of a semisubmersible model under focused wave groups: Experimental investigation

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Journal of Ocean Engineering and Science 2017年第3期2卷 161-171页

作者： Michael Banks Nagi Abdussamie National Centre for Maritime Engineering and Hydrodynamics Australian Maritime CollegeUniversity of TasmaniaLauncestonTAS 7250Australia

In recent years,extreme wave events have occurred more frequently than have been predicted using theoretical methods.It is,therefore,a requirement to investigate the impact of these events on coastal and offshore structures.This paper reports on results of an experimental investigation into the interaction between unidirectional waves and a horizontally moored semisubmersible model.The target crest height was created at a focal point and time using the focused wave technique.Different values of wave steepness were tested in order to ascertain the nonlinear effects on the quality of waves generated by a piston-type wavemaker.The measured crest height was in good agreement with the theoretical one within 4%relative error.The magnitudes of heave and pitch motions of the model were found to increase as the wave steepness increased.Overall,the paper contributes towards establishing the application of focused wave technique to floating offshore platforms.

关键词： focused wave Offshore platforms Dynamic response

Numerical Simulation of focused wave and Its Uncertainty Analysis

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Journal of Shanghai Jiaotong university(Science) 2018年第4期23卷 475-481页

作者：柏君励马宁顾解忡 State Key Laboratory of Ocean Engineering Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration Shanghai Jiao Tong University

On the basis of the transient water wave(TWW) theory,focused wave is generated in the circulating water channel.Numerical simulation of the focused wave is carried out by solving the Reynolds averaged NavierStokes(RANS) equations.The dynamic grid technique is adopted to simulate the motion of the wave maker,and the volume of fluid(VOF) method is used to capture the free surface of the wave.The simulation results are compared with the measured data,and good agreement is obtained.For quantitative estimation of the numerical simulation error and uncertainty,the uncertainty analysis method recommended by the International Towing Tank Conference(ITTC) procedure is performed for the simulation results of the surface elevations at different positions.Both grid-convergence and time-step-size convergence studies are conducted using three types of grids and time step sizes.The simulation results are all monotonously convergent in the verification procedure,and the validations of the simulated surface elevations with the positions at 3.5,4.0 and 4.5 m are all achieved by comparing with the validation uncertainty.It is found that the numerical simulation errors caused by the grid and time-step-size in the convergence studies have the same order of magnitude.In addition,the numerical errors and uncertainties for the surface elevations at different positions are compared and discussed in detail.This paper presents the first attempt to carry out the uncertainty analysis of the simulation of focused wave,and the effectiveness of the proposed verification and validation procedures in the uncertainty analysis is demonstrated.

关键词： focused wave uncertainty analysis verification validation Reynolds averaged Navier-Stokes(RANS) equations

Numerical Study of the High-Frequency wave Loads and Ringing Response of A Bottom-Hinged Vertical Cylinder in focused waves

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China Ocean Engineering 2020年第4期34卷 513-525页

作者： ZHANG Yi TENG Bin State Key Laboratory of Coastal and Offshore Engineering Dalian University of TechnologyDalian 116024China

This paper presents a numerical study on the high-frequency wave loads and ringing response of offshore wind turbine foundations exposed to moderately steep transient water waves.Input wave groups are generated by the technique of frequency-focusing,and the numerical simulation of focused waves is based on the Newwave model and a Fourier time-stepping procedure.The proposed model is validated by comparison with the published laboratory data.In respect of both the wave elevations and the underlying water particle kinematics,the numerical results are in excellent agreement with the experimental data.Furthermore,the local evolution of power spectra and the transfer of energy into higher frequencies can be clearly identified.Then the generalized FNV theory and Rainey’s model are applied respectively to calculate the nonlinear wave loads on a bottom-hinged vertical cylinder in focused waves.Resonant ringing response excited by the nonlinear high-frequency wave loads is found in the numerical simulation when frequency ratios(natural frequency of the structure to peak frequency of wave spectra)are equal to 3–5.Dynamic amplification factor of ringing response is also investigated for different dynamic properties(natural frequency and damping ratio)of the structure.

关键词： high-frequency wave loads ringing response focused wave vertical cylinder

Simulation of Horizontal-Two-Dimension focused waves Using A Two-Layer Boussinesq-Type Model

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China Ocean Engineering 2023年第5期37卷 725-737页

作者： ZOU Wen-feng WANG Ping LIU Zhong-bo FANG Ke-zhao SUN Jia-wen ZHANG Ning-chuan Key Laboratory of coastal and offshore engineering Dalian University of TechnologyDalian 116024China State Environmental Protection Key Laboratory of Marine Ecosystem Restoration National Marine Environmental Monitoring CenterDalian 116023China Dalian Maritime University College of Transportation EngineeringDalian 116024China

Accurate simulation of the horizontal-two-dimension(H2D)focused wave group in deep water requires high accuracy of a numerical model.The two-layer Boussinesq-type model(Liu and Fang,2016;Liu et al.,2018)with the highest spatial derivative of 2 has high accuracy in both linear and nonlinear properties.Based on the further development of the velocity equations(Liu et al.,2023),the H2D numerical model for water waves is established with the prediction-correction-iteration model in the finite difference method,and a composite fourth-order Adams-Bashforth-Moulton scheme is used for time integration.The wave generation method proposed by Hsiao et al.(2005)is applied and calibrated in this H2D model.The numerical calculations lead to the following three main conclusions:First,compared with the analytical solution of Stokes linear waves,the calculated velocity profiles show higher accuracy by using the improved velocity formulas.Second,the simulations of the focused multidirectional wave group are carried out,and good agreements are found,demonstrating that the present H2D numerical model shows high accuracy in simulating focused multidirectional wave groups,and the effectiveness of the improved velocity formulas is also validated.Furthermore,the velocity profiles throughout the computational domain at the time of maximum wave crest are given.Finally,the FFT method is used to obtain the amplitude with different frequencies for several locations,and the changes of the wavelet energy spectrum at different locations are presented for several cases.

关键词： focused wave horizontal-two-dimension model finite difference method nonlinear property

Nonlinear Dynamic Behaviors of A Floating Structure in focused waves

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China Ocean Engineering 2015年第6期29卷 807-820页

作者：曹飞凤赵西增 Institute of Harbor-Channel and Coastal Engineering Department of Civil EngineeringZhejiang University of Technology Ocean College Zhejiang University State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering Nanjing Hydraulic Research Institute

Floating structures are commonly seen in coastal and offshore engineering. They are often subjected to extreme waves and, therefore, their nonlinear dynamic behaviors are of great concern. In this paper, an in-house CFD code is developed to investigate the accurate prediction of nonlinear dynamic behaviors of a two-dimensional（2-D） box-shaped floating structure in focused waves. Computations are performed by an enhanced Constrained Interpolation Profile（CIP）-based Cartesian grid model, in which a more accurate VOF（Volume of Fluid） method, the THINC/SW scheme（THINC： tangent of hyperbola for interface capturing; SW： Slope Weighting）, is used for interface capturing. A focusing wave theory is used for the focused wave generation. The wave component of constant steepness is chosen. Comparisons between predictions and physical measurements show good agreement including body motions and free surface profiles. Although the overall agreement is good, some discrepancies are observed for impact pressure on the superstructure due to water on deck. The effect of grid resolution on the results is checked. With a fine grid, no obvious improvement is seen in the global body motions and impact pressures due to water on deck. It is concluded that highly nonlinear phenomena, such as distorted free surface, large-amplitude body motions, and violent impact flow, have been predicted successfully.

关键词： focused wave CIP method wave-structure interaction VOF method free surface flow wave breaking

Numerical Study of focused wave Impact on a 2-D Floating Body Using CIP-based Method

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Numerical Study of Focused Wave Impact on a 2-D Floating Bod...

AN IMPROVED NUMERICAL METHOD FOR CALCULATIONS IN wave KINEMATICS

第二十三届全国水动力学研讨会暨第十届全国水动力学学术会...

作者： Xizeng Zhao,Sheng Dong College of Engineering,Ocean University of China,Qingdao 266100,China,

＜正＞In rough seas,marine structures such as ship,platform,etc.frequently experience highly nonlinear phenomena such as slamming,water on deck,wave impact by green water and capsizing due to large-amplitude waves.Investigation of such wave-body interaction problem is of considerable importance in engineering application.This paper uses a constrained interpolation profile（CIP）-based Cartesian grid method to numerically investigate the focused wave impact on a two-dimensional floating body,which is validated against to a newly performed experiment.In the experiment,focused wave is generated and a box-shaped floating body with a superstructure is utilized.Validation computations on the experiment are performed by the CIP-based Cartesian grid method,in which the THINC scheme（THINC,tangent of hyperbola for interface capturing）,is used for interface capturing.The highly nonlinear wave-body interactions,including large amplitude body motions and water on deck are numerically investigated and compared with experimental data. Good agreements are achieved to show the ability of the presented model for extremely nonlinear wave-body interactions.

关键词： focused wave CIP method wave-body Interaction Water on deck wave impact

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Journal of Hydrodynamics 2009年第6期21卷 826-834页

作者： SUN Yi-yan LIU Shu-xue LI Jin-xuan State Kay Laboratory of Coastal and Offshore Engineering Dalian University of Technology Dalian 116024

The prediction of wave kinematics is a necessary basis for ocean engineering design. In this article, an improved method to calculate the wave kinematics especially in the crest region is presented. This method is based on the local approximation method. According to one measured wave surface, the proposed solution focuses on a Fourier series expansion in a somewhat larger segment of the wave surface record. The horizontal and vertical kinematics under the wave crest can be directly predicted. Good agreement between the numerical results and the theoretical Stokes waves verifies the validity of the numerical model. The effectiveness of the numerical method is also proved by the calculation of the wave kinematics of the laboratory focused wave groups.

关键词： Fourier series expansion wave kinematics focused wave